Step 4: Display Summaries

• Jun 24, 2020
• 3 minutes to read

You should enable data operations after you bind the GridControl to a virtual source.

In this step, we describe how to display summaries:

• You process summaries in the virtual source.
• Then you display summaries in the GridControl.

Note

The Issues Service is used as an example of a data source in this tutorial.

Tip

Demos:

• Infinite Scrolling Source - Step 4
• Paged Source - Step 4

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Overview

The Issues Service allows you to obtain:

• A total count of rows.
• The last created object’s datetime.

C#

public class IssuesSummaries {   
    public int Count { get; private set; }
    public DateTime? LastCreated { get; private set; }
}

Display Summaries

1. Process summaries in the virtual source:

   • Handle the InfiniteAsyncSource.GetTotalSummaries event.
   • Use the Issues Service‘s GetSummariesAsync method to get summaries from the data source.
   • Use the GetSummariesEventArgsBase.Summaries property to get the GridControl‘s summary items.
   • Specify the GetSummariesAsyncEventArgs.Result property to return summaries that correspond to the GridControl‘s summary items.
   C#

   source.GetTotalSummaries += (o, e) => {
       e.Result = GetTotalSummariesAsync(e);
   };
   static async Task<object[]> GetTotalSummariesAsync(GetSummariesAsyncEventArgs e) {
       IssueFilter filter = MakeIssueFilter(e.Filter);
       var summaryValues = await IssuesService.GetSummariesAsync(filter);
       return e.Summaries.Select(x => {
           if(x.SummaryType == SummaryType.Count)
               return (object)summaryValues.Count;
           if(x.SummaryType == SummaryType.Max && x.PropertyName == "Created")
               return summaryValues.LastCreated;
           throw new InvalidOperationException();
        }).ToArray();
   }
   

2. Set the DataViewBase.ShowFixedTotalSummary property to true to show the Fixed Summary Panel:

   XAML

   <dxg:TableView ShowFixedTotalSummary="True" />
   

3. Specify the GridControl.TotalSummary property to display total summaries in the GridControl:

   XAML

   <dxg:GridControl.TotalSummary>
       <dxg:GridSummaryItem SummaryType="Count" Alignment="Right"/>
       <dxg:GridSummaryItem SummaryType="Max" FieldName="Created" 
                            DisplayFormat="{}Last created: {0}" Alignment="Right"/>
   </dxg:GridControl.TotalSummary>
   

Display Custom Summaries

In the example below, the Issues Service can calculate the Median and StdDev values:

C#

public class IssuesSummaries {
    // ...
    public double VotesMedian { get; private set; }
    public double VotesStdDev { get; private set; }
}

1. Process summaries in the virtual source:

   C#

   static async Task<object[]> GetTotalSummariesAsync(GetSummariesAsyncEventArgs e) {
       IssueFilter filter = MakeIssueFilter(e.Filter);
       var summaryValues = await IssuesService.GetSummariesAsync(filter);
       return e.Summaries.Select(x => {
           if(x.SummaryType == SummaryType.Count)
               return (object)summaryValues.Count;
           if(x.SummaryType == SummaryType.Max && x.PropertyName == "Created")
               return summaryValues.LastCreated;
   
           // Custom Summaries
           if(x.SummaryType == SummaryType.Custom && x.PropertyName == "Votes") {
               var tag = x.Tag as string;
               if(tag == "Median")
                   return summaryValues.VotesMedian;
               if(tag == "StdDev")
                   return summaryValues.VotesStdDev;
           }
           throw new InvalidOperationException();
       }).ToArray();
   }  
   

2. Display summaries in the GridControl:

   Xaml

   <dxg:GridControl.TotalSummary>
       <dxg:GridSummaryItem SummaryType="Count" Alignment="Right"/>
       <dxg:GridSummaryItem SummaryType="Max" FieldName="Created" 
                            DisplayFormat="{}Last created: {0}" Alignment="Right"/>
       <!-- Custom Summaries -->
       <dxg:GridSummaryItem SummaryType="Custom" Tag="StdDev" FieldName="Votes" 
                            DisplayFormat="{}Votes StdDev={0}" Alignment="Right"/>
       <dxg:GridSummaryItem SummaryType="Custom" Tag="Median" FieldName="Votes" 
                            DisplayFormat="{}Votes Median={0}" Alignment="Right"/>
   </dxg:GridControl.TotalSummary> 
   

Continue or Review

• To go to the next tutorial step, see Step 5: Enable Data Editing.
• To return to the previous tutorial step, see Step 3: Enable Filtering.